1. Field of the Invention
The present invention relates to a piezoelectric vibrating reed made of a piezoelectric material, such as quartz or lithium tantalate, a piezoelectric vibrator having the piezoelectric vibrating reed, and an oscillator, an electronic device, and a radio-controlled clock each having the piezoelectric vibrator, as well as a manufacturing method of the piezoelectric vibrating reed.
2. Description of the Related Art
Recently, a piezoelectric vibrator utilizing quartz or the like is used in a cellular phone and a portable information terminal as the time source, the timing source of a control signal, a reference signal source, and the like. The piezoelectric vibrator of this type is proposed in a variety of forms, and a piezoelectric vibrator having a turning-fork type piezoelectric vibrating reed is one example. This piezoelectric vibrating reed is a vibrating reed that allows a pair of vibrating arms disposed in parallel to each other to vibrate at a predetermined resonance frequency in a direction to move closer to or away from each other.
As represented by cellular phones, various electronic devices having the piezoelectric vibrator have become smaller in recent years. Accordingly, there is a demand for the piezoelectric vibrating reed of the piezoelectric vibrator to be further reduced in size. Therefore, the piezoelectric vibrating reed is expected to have a structure such that the length of the vibrating arm or base portion thereof is decreased so as to have a shorter total length.
However, when the total length of the piezoelectric vibrating reed is reduced by decreasing the length of the base portion, mounting performance thereof will decrease, and the vibrating arm is likely to vibrate unstably. Thus, vibration loss (leakage of vibration energy) through the base portion can occur easily. For this reason, there is concern about increasing the CI value (crystal impedance). Particularly, since there is an influence of vibration loss, the method of decreasing the length of the base portion is not considered a practically effective method.
Therefore, in order to achieve miniaturization by decreasing the total length of the piezoelectric vibrating reed, it is effective to decrease the length of the vibrating arm rather than the base portion. However, when the length of the vibrating arm is decreased, the R1 value (series resonance resistance value) increases and the vibration characteristics tend to deteriorate. Particularly, since the R1 value is proportional to the effective resistance value Re, if the R1 value increases, it is difficult to operate the piezoelectric vibrating reed at low power.
Therefore, in order to reduce the R1 value, JP-A-2004-120556 discloses a piezoelectric vibrating reed in which groove portions are formed on both principal surfaces (top and back surfaces) of a pair of vibrating arms along the longitudinal direction of the vibrating arms.
This piezoelectric vibrating reed is formed such that the pair of vibrating arms have an H-type section due to the presence of the groove portions, so that excitation electrodes face each other at a very small distance. For this reason, compared with a case where no groove portions are formed, an electric field can be applied more efficiently and vibration loss can be reduced. Therefore, it is possible to improve vibration characteristics and suppress the R1 value to a low value.
As described above, in order to achieve miniaturization of the piezoelectric vibrating reed while suppressing an increase of the R1 value, it is an effective means to form groove portions in the vibrating arms and decrease the lengths of the vibrating arms.
However, since the groove portions are formed on the principal surfaces of the vibrating arms, the surface area of the principal surfaces of the vibrating arms will decrease. For this reason, the electrode pattern is likely to have a fine pitch, and thus, there is a high risk of midway disconnection during the patterning. This will be described in detail below.
As shown in FIG. 24, a piezoelectric vibrating reed 200 includes a pair of excitation electrodes 203 formed in a pair of vibrating arms 201a and 201b, a mount electrode 204 formed in a base portion 202, and an extraction electrode 205 connecting the mount electrode 204 and the pair of excitation electrodes 203 together.
Among these electrodes, the pair of excitation electrodes 203 are electrodes that allow the pair of vibrating arms 201a and 201b to vibrate in a direction to move closer to and away from each other when a predetermined voltage is applied thereto via the mount electrode 204. One excitation electrode 203 is mainly formed on the groove portion 206 of one vibrating arm 201a and on both side surfaces of the other vibrating arm 201b. The other excitation electrode 203 is mainly formed on the groove portion 206 of the other vibrating arm 201b and both side surfaces of one vibrating arm 201a. 
Moreover, the excitation electrode 203 formed on the side surfaces of one vibrating arm 201a is patterned on the groove portion 206 of the other vibrating arm 201b after being led out towards the principal surface of the base portion 202 at the vicinity of a fork portion 207.
The respective electrodes are patterned by exposure through a mask. For this reason, in order to perform patterning at high accuracy, high exposure position accuracy is required.
However, in practical cases, the exposure position accuracy will have errors due to mask positioning accuracy or lens aberrations during exposure. Therefore, the electrode patterns may be shifted from desired positions. Particularly, when the electrode patterns are shifted in the direction indicated by the arrow A in FIG. 24, a lead-out portion 210 of the excitation electrode 203 led out from the side surface of the vibrating arm 201a towards the principal surface of the base portion 202 will be caught at the fork portion 207 as shown in FIG. 25. Since the fork portion 207 is a portion where an uneven surface can occur easily, it is generally difficult to form electrodes on the fork portion. For this reason, the excitation electrodes 203 may be disconnected at the fork portion 207, and the excitation electrodes 203 formed on the side surfaces of one vibrating arm 201a are not connected to the groove portion 206 of the other vibrating arm 201b. 
When the excitation electrodes 203 are disconnected midway, the vibrating arms 201a and 201b will not vibrate, resulting in defective units. Therefore, when exposure is performed, it is necessary to align the exposure positions with strictly high accuracy so that the excitation electrodes are not disconnected at the fork portion 207. For this reason, it is difficult to achieve high manufacturing efficiency.